Classifying apparatus



Jan. 11, 1966 s. c. RUSTAD 3,228,521

CLASSIFYING APPARATUS Filed March 29, 1963 2 Sheets-Sheet l (D IO (O L N g n E W g o g INVENTOR.

1 8 h STANLEY C. RUSTAD Ml J 16744 ATTOR N EY Jan. 11, 1966 s. c. RUSTAD 3,228,521

CLASSIFYING APPARATUS Filed March 29, 1963 2 Sheets-Sheet 2 O o w 0 8 f? PF no 9 J \VV [Uh [1 'm as. r

P0 S2 LL g INVENTOR.

Q STANLEY c. RUSTAD C? fl-Zq/ 6. M

ATTORNEY United States Patent 3,228,521 CLASSIFYING APPARATUS Stanley C. Rustad, Minneapolis, Minn., assignor to General Mills, Inc., a corporation of Delaware Filed Mar. 29, 1963, Ser. No. 269,110 Claims. (Cl. 209-322) The present invention relates to improved classifying apparatus, and more particularly to an improved vibratory or reciprocating sifter for classifying finely ground or powdered materials, such as flour milling stocks.

Sifting devices are known in the prior art in which stock is conveyed across a screen or sifting surface by suitable reciprocation or vibration of the sifting unit. During such movement, the stock is classified into separate fractions of different particle size. In such siftcrs the sifting surface is often enclosed in an outer box or frame to prevent escape of fine particles of stock. Both the box and enclosed sifting surface are then subjected to rapid vibratory reciprocation to convey the material across the sifting surface and obtain the desired separation.

One of the problems in the application of such a sifter to finely ground or powdered materials is that of irregularity or surging in the sifting and conveying action of the stock on the surface. Such surging has been found to involve the adverse effect of variations in the instantaneous dynamic air pressures above and below the sifting surface. Such pressure changes may cause the stock to tend to be held fast to the screen when it should be free to slide, and conversely to be blown upwardly away from the screen when it should be in contact with it. The problem is particularly encountered at rapid frequencies of reciprocation, e.g. of the order of six strokes per second.

With the problems of the prior art in view, it is an object of this invention to provide such an apparatus with improved means to eliminate, or compensate for, a tendency of the apparatus to create adverse dynamic pressure etfects above and below the screen, and to create desired pressure effects above and below the screen, which means can readily be adapted to operate effectively with various arrangement and configurations of the sifting apparatus, and under various operating conditions thereof, to achieve the desired sifting and conveying action.

It is a more specific object to provide such means with a cyclic compensating movement, the phase, amplitude, and in some cases the frequency of which can be arranged or adjusted with respect to the sifting movement of said apparatus and in some cases to other portions of such means, in a manner to aid in accomplishing the desired sifting and conveying action.

These and other objects and features of the invention will be more readily understood and apreciated from the following detailed description of the preferred embodiments thereof selected for purposes of illustration and shown in the accompanying drawings, in which;

FIGURE 1 is a semi-schematic side elevational view, drawn partly in section, of a sifting apparatus embodying preferred teachings of my invention.

FIGURE 2 is a transverse sectional view taken on line 22 of FIG. 1.

FIGURE 3 is a view similar to FIG. 1, illustrating a second embodiment of my invention, and

FIGURE 4 is a fragmentary horizontal sectional view taken on line 44 of FIG. 3.

As shown in FIGS. 1 and 2, there is a box or body portion 10, comprising a top, bottom, and two side walls, designated 12, 14, 16, and 18 respectively. The front of the body is provided with an end wall 20, while the rear is closed by an upper feed plate 22 and a lower 3,228,521 Patented Jan. 11, 1966 movable wall member 24a, which in the present embodiment is one of a plurality (as shown herein three) movable Wall or partition members 24a, b and c, the function of which will be disclosed more fully hereinafter. This body provides containing means defining an enclosure designed for longitudinal reciprocation. For this purpose, the sifter body is suspended by swinging hanger members 26. The lower ends of hangers 26 are pivotally connected at 28 to the sifter body, while the upper ends of hangers 26 are pivotally supported at 30 from a suitable frame or ceiling member 32.

The sifter body 10 is reciprocated by a driving rod 34, one end of which is pivotally connected at 36 to a transverse mounting bar 38 secured to the body sidewalls 16 and 18, and the other end of which is driven by an eccentric 40 mounted on a drive shaft 42. The drive shaft 42 is in turn driven by any suitable power source, such as motor 44, provided with a manually operable speed adjustment handle 46. Thus the sifter can be reciprocated longitudinally at a desired frequency and at a desired amplitude (by adjusting the throw of the eccentric 40) to achieve a desired conveying movement and classification. To impart to the aforementioned movable wall members 24a, b and c, a reciprocating movement of a selected phase and amplitude, there is provided a second eccentric 48 which is mounted on the drive shaft 42 and has a drive rod 50 that is pivotally connected as at 51 to the rear wall member 24a.

The actual sifting is done by a sifting surface or screen of known type such as the metal or cloth screen shown schematically at 52. This sifting screen extends longitudinally across the major portion of the box 10 and thus effectively divides the box into upper and lower chambers 54 and 56. The rear or inlet end of this screen is secured to the lower end of the aforementioned feed plate 22, which is sloped downwardly and forwardly so that flour stock received from a surmounting feed conduit 58 in the top wall 12 will be properly directed by the feed plate 22 onto the screen 52. The front or discharge end of the screen 52 is secured to the top end of a downwardly reaching discharge plate 60, which forms with the front end wall 20 and the adjacent portions of the side walls 16 and 18 a suitable outlet passage 62 from the upper retaining chamber 54 for the flour stock retained on the screen 52.

The aforementioned movable wall members 24a, b and c extend transversely across respectively, the rear, middle, and front of the lower collecting chamber 56, with the rear and front walls thus defining the end limits of the lower chamber 56, and the center wall 24b partitioning this chamber into rear and front lower chamber portions 56:: and 56b, respectively. Each of the three wall members 24a, b and 0 comprises a plate 64 joined by a respective peripheral membrane 66 to a respective surrounding frame 68 which is fixed to the box 10 and extends circumferentially about a transverse section of the lower chamber 56 at which that frame is located. That is to say, each of these three frames extends along the bottom and side walls 14, 16, and 18, while the top part of the rear, middle and front frame members 68 fits against the bottom side of, respectively, the feed plate 22, the screen 52, and the discharge plate 60. Thus, each of the flexible membranes 66 forms an effective seal transversely of the lower chamber 56, while permitting its related plate 64 to reciprocate longitudinally.

When it is desirable (as in this first embodiment) that the three movable wall members 24a, b and c reciprocate together, they are fixed one to another by means of longitudinal tie rods 70 which are threaded into related socket members 72 that are fixed to the plate members 64. Two discharge conduits 74a and 74b are provided in the bottom wall 14 immediately behind, respectively, the wall members 24b and 240 to furnish each of the lower chamber portions 56a and 56b with a suitable outlet for the flour stock which passes through the sifting screen 52. Although not shown herein, suitable means can be provided to maintain the plates 64 at the desired locations in the lower chamber, as, for example, in the form of slide mountings for the tie rods 70. Also, to illustrate simply the manner in which the walls 24a, b and c are movably mounted, these walls are shown in broken lines at a rear position and a middle position, and in full lines in a forward position, while no attempt has been made to show the corresponding positions of the box 10. However, it is to be understood that in the particular arrangement shown in FIGS. 1 and 2, as the plates 64 move to these positions, the box and hence the surrounding frames 68 will be moving oppositely, and so the outermost portions of the membranes 66 will be moving in opposition to the plates 64, whereas in FIG. 1 the outermost portions of the membrane 66 are shown as remaining stationary.

In operation, the motor 44 turns the eccentric 40 by means of drive shaft 42 to reciprocate the sifting box 19, While flour stock to be sifted is fed through the feed inlet provided by the conduit 58 and into the upper chamber 54. As is commonly done in the prior art, each of the hangers 26, in the middle position of its reciprocating movement has its lower pivotal connection 28 spaced moderately forward of the upper connection 30, so that the reciprocating path of the box 10 is slanted moderately upward and forward, as indicated by the double headed arrow 76. The result is that stock which enters the conduit 58 is then conveyed longitudinally along the sifting surface 52, as shown at 78. Particles too coarse to pass through the screen proceed to the discharge end of the upper retaining chamber 54 and pass through the outlet passage 62, which is suitably connected to a subsequent processing machine, receptacle, or conveyor. The finer particles of stock which pass through the screen 52 are conveyed along the bottom wall 14 to either of the outlets 74a or 74b. If desired, the rear portion of the screen 52 may be of finer mesh than the front portion, so that the fraction of flour stock passing into the rear lower collecting chamber portion 56a is of finer particle size than that passing into the front chamber portion 56b.

As the eccentric 40 recipr-ocates the box 10, the eccentric 48, also driven from the shaft 42, will reciprocate the wall 24a (and consequently the walls 24b and c) at the same frequency as the box 10. However, in this particular arrangement shown in FIGS. 1 and 2, the eccentric 48 is so positioned with respect to the eccentric 40 that the extreme throw positions of the eccentrics 40 and 48 are approximately 180 apart, which accordingly puts the reciprocating movement of the box 10 approximately 180 out of phase with that of walls 24a, b and 0.

By so reciprocating these walls 24a, b and c, the undesirable instantaneous pressures which would otherwise be created in the lower chamber by virtue of the reciprocating motion of the box 10 are relieved. For example, if the rear wall 24a were rigid with the box 10, when the box 10 moves forwardly and slightly upward in its cycle of reciprocation, the air immediately in front of the wall 24a would experience a slight increase in pressure which would have a buoying or lifting effect on the stock resting on the rear portion of the screen 52. This would hinder the screen, as it moves forwardly, from imparting to the stock at the rear end of the screen an increment of forward travel, which is necessary for the stock to achieve the desired sifting and conveying movement forwardly along the screen. A similar effect would be produced immediately in front of the wall 24b if it were stationary with box 10.

For several practical reasons (e.g. the outer portions of the membranes 66 moving with the box 10 and thus acting adversely on the air columns, possible leakage, etc), and

for other reasons which are not fully understood but which relate to the dynamics of the waves created in the reciprocating box 10, and to periodic pressure differentials which are desired to be created between the chambers, it is sometimes desirable to over-compensate for the pressures created by the reciprocating motion of the box 19. Because of this the eccentric 48 may be employed to actually mOVe the wall members 24a, b and c against the air columns enclosed in chambers 56:: and b to create air movements in opposition to those undesirable air movements which tend to be created by reciprocation of the box 10. Also for reasons not fully understood, it is sometimes desirable to have the counteracting movements of the walls 24a, b and c to be in a cycle not diametrically out of phase with the reciprocating cycle of the box It}. For this reason, the lock (shown schematically at between the eccentric 48 and the drive shaft 42 is capable of being placed in various locking positions as at 82 to vary the relative angular positions of the extreme throw of the eccentrics 4b and 48, and thus vary the phase relationship thereof. It is to be understood that the eccentric 48, as well as the eccentric 40, is also capable of replacement or adjustment with respect to the drive shaft 4-2 so as to vary the length of the throw and thus vary accordingly the amplitude of the reciprocating motion of movable walls 24a, b and c.

A second embodiment of my invention is illustrated. in FIGS. 3 and 4. Components of the second embodiment which are similar to those of the first embodiment will be given like numerical designations, with a prime designation distinguishing those of the second embodiment. It can readily be seen that the box 10 has the same overall configuration of the box 10 of the first embodiment, and has a sifting screen 52 partitioning the box 10' into upper and lower chambers 54' and 56'. The feed conduit 58', the outlet passage 62', the motor 44', and the hanger members 26 all function in substantially the same manner as their counterparts of the first embodiment to achieve the desired sifting and conveying action of the flour stock.

The lower chamber 56' is provided with two movable wall members 24d and 24e, which are arranged and positioned similarly to, respectively, the rear and front wall members 24a and 240 of the first embodiment so as to close chamber 56' at the rear and the front. The rear movable wall member 24d is reciprocated by means other than that which reciprocates the box 10. This is accomplished through a multi-speed transmission driven from the motor 44' by a chain and sprocket drive 92 to turn eccentric 48 through drive shaft 94'. Separate drive means is conveniently provided for the front movable wall member 242 in the form of a drive rod 100, the rear end of which is pivotally connected to wall Me and the front end of which is secured to an eccentric 102, which in turn is driven by a drive shaft 194 from a motor 106. Thus the frequency as well as the amplitude and phase of the reciprocating movement of each of the wall members 24d and 24e can be varied independently of the movement of both the box 10' and the other wall member 24d or 24s. To permit the rod 1% to reach through the upper chamber discharge passage 62', a small protective housing member 108, open at both ends, is placed between the discharge plate 60' and the front end wall 20. Since the lower chamber 56' is, in this embodiment, not partitioned into sub-chambers, only one lower chamber outlet is provided, as at 740 at the front end of lower chamber 56'.

The sifting action in the second embodiment is generally the same as in the first embodiment, with the flour stock being fed into the inlet conduit 58', being classified by the sifting screen 52, and being discharged through the outlets 62' and 740. The intended effect of reciprocating the walls 24d and 242 of the second embodiment is, as in the first embodiment, to relieve the undesirable instantaneous pressures which would otherwise be created by virtue of the reciprocating motion of the box 10' and. thus obtain the desired sifting and conveying action, and in some instances to create desirable periodic air pressure differentials between the chambers 54' and 56.

For reasons not yet fully understood, but which relate to the pressure effects created within the sifting apparatus, it may be desired that under certain operating conditions the phases and amplitudes, and sometimes the frequencies of the cyclic movements of the movable wall members 24d and 24a differ from each other or from that of the sifting apparatus. It is for this reason that the movable wall members 24d and Me of the second embodiment are each provided with drive means whose adjustment is independent from that of the box and independent of each other.

To enlarge upon this consideration, it is recognized that the adverse or the dwirable pressure effects at one portion of the sifting apparatus may be quite different from those at another portion. For example, in this second embodiment, the presence of the discharge outlet 740 at the front end of the lower chamber 56' would very likely affect the instantaneous pressures in that area differently from the area proximate the rear movable wall member 24d. Thus in the arrangement of the second embodiment, with the rear wall member He having drive means adjustable independent of both the box 10' and the wall member 24d, the phase, amplitude and frequency of the front wall member 242 can each be varied independently of the reciprocating movement of both the rear wall member 24d and the box 10', to obtain the desired sifting and conveying action of flour stock.

As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Now therefore I claim:

1. In a vibratory classifying unit comprising a sifting and conveying surface having receiving and discharge ends, a body enclosing said surface in a manner to provide substantially closed upper and lower chambers above and below said surface, and having inlet means at the receiving end of said surface and discharge means at the discharge end of said surface, means for reciprocating said surface and at least a part of said body as a unit longitudinally along a desired path and thereby conveying stock from said receiving end to said discharge end while classifying the stock by means of said surface, the improvement comprising wall means at said lower chamber and extending transversely of said reciprocating path, said wall means comprising a plurality of wall members spaced longitudinally of one another, said wall means being movable with respect to said surface, and driving means for reciprocating said wall means longitudinally with predetermined phase, amplitude, and frequency characteristics, thereby generating desired periodic pressures proximate to said surface.

2. The apparatus as recited in claim 1, wherein said wall members are connected to each other for simultaneous movement by said driving means.

3. The apparatus as recited in claim 1, wherein there are at least two wall members and there are means for adjusting at least one of the phase, amplitude and frequency characteristics of said wall members with respect to each other.

4. In a vibratory classifying unit comprising a sifting and conveying surface having receiving and. discharge ends, a body enclosing said surface in a manner to provide substantially closed upper and lower chambers above and below said surface, and having inlet means at the 'receiving end of said surface and discharge means at the discharge end of said surface, means for reciprocating said surface and at least a part of said body as a unit longitudinally along a desired path and thereby conveying stock from said receiving end to said discharge end while classifying the stock by means of said surface, the improvement comprising means extending transversely and defining a portion of said lower chamber proximate the receiving end of said surface, said defining means being movable with respect to said surface along a path toward and away from air in said lower chamber near the receiving end of said surface, and driving means for reciprocating said defining means along said path with predetermined phase, amplitude, and frequency characteristics, thereby generating desired periodic pressures proximate to said surface, and also comprising second means defining a portion of said lower chamber proximate the discharge end of said sifting and conveying surface, said second defining means being movable with respect to said surface along a path toward and away from air in said lower chamber, and second driving means for reciprocating said second defining means along said path with predetermined phase, amplitude and frequency characteristics.

5. The apparatus as recited in claim 4, wherein at least one of the phase, amplitude and frequency characteristics of one of said defining means may be adjusted with respect to that of the other defining means.

References Cited by the Examiner UNITED STATES PATENTS 2,903,135 9/1957 Dryg 209--236 3,021,952 2/ 1962 Powell 209240 FOREIGN PATENTS 84,764 5/ 1895 Germany.

13,882 9/1888 Great Britain. 345,275 3 1931 Great Britain.

72,275 3/ 1917 Switzerland.

HARRY B. THORNTON, Primary Examiner.

HERBERT L. MARTIN, R. HALPER,

Assistant Examiners, 

1. IN A VIBRATORY CLASSIFYING UNIT COMPRISING A SIFTING AND CONVEYING SURFACE HAVING RECEIVING AND DISCHARGE ENDS, A BODY ENCLOSING SAID SURFACE IN A MANNER TO PROVIDE SUBSTANTIALLY CLOSED UPPER AND LOWER CHAMBERS ABOVE AND BELOW SAID SURFACE, AND HAVING INLET MEANS AT THE RECEIVING END OF SAID SURFACE AND DISCHARGE MEANS AT THE DISCHARGE END OF SAID SURFACE, MEANS FOR RECIPROCATING SAID SURFACE AND AT LEAST A PART OF SAID BODY AS A UNIT LONGITUDINALLY ALONG A DESIRED PATH AND THEREBY CONVEYING STOCK FROM SAID RECEIVING END TO SAID DISCHARGE END WHILE CLASSIFYING THE STOCK BY MEANS OF SAID SURFACE, THE IMPROVEMET COMPRISING WALL MEANS AT SAID LOWER CHAMBER AND EXTENDING TRANSVERSELY OF SAID RECIPROCATING PATH, SAID WALL MEANS COMPRISING A PLURALITY OF WALL MEMBERS SPACED LONGITUDINALLY OF ONE ANOTHER, SAID WALL MEANS BEING MOVABLE WITH RESPECT TO SAID SURFACE, AND DRIVING MEANS FOR RECIPROCATING SAID WALL MEANS LONGITUDINALLY WITH PREDETERMINED PHASE, AMPLITUDE, AND FREQUENCY CHARACTERISTIC, THEREBY GENERATING DESIRED PERIODIC PRESSURES PROXIMATE TO SAID SURFACE. 